They can apply for their proof of citizenship through the mail, see
http://www.cic.gc.ca/english/citizenship/proof.asp They would go through the Canadian embassy closest to where they live. You will notice that the processing time stated is over a year. If they have plans to move to Canada, they can ask for their citizenship cards to be expedited and they would get them faster. Once they get the citizenship cards, they can get Canadian passports.
It is not an option for you to apply for their PR. One of the reasons is that they are already citizens, the other is that even if they weren't, they are too old to be sponsored for PR, they are not dependent children any more.